This invention relates to a die casting machine in which a plurality of mold opening and closing units holding metal molds are rotated by a rotary table and a casting operation is performed in successive steps in a plurality of operation stations disposed in an equally spaced relationship on the locus of the rotational movement of the units.
The applicant has previously developed a rotary die casting machine with the object of substantially enhancing its productivity (Japanese patent application Sho 61(1986)-195766). The die casting machine is so designed that mold opening and closing units for holding metal molds are mounted in positions in a spaced relationship in the outer periphery of a rotary table dividing the periphery of the table and as the rotary table rotates, the mold opening and closing units are stopped in positions in alignment with a plurality of operation stations disposed on the locus of the mold opening and closing units to perform different operations in succession.
The previously proposed die casting machine will be described referring to FIG. 1. The die casting machine 1 comprises a rotary table 14 and a first station 2, a second station 3 and a third station 4 disposed about the periphery of the rotary table 14. The center lines of the first station 2, the second station 3 and the third station 4 are disposed at an angle of 120.degree. to each other as shown by L1, L2 and L3, respectively. As more clearly shown in FIG. 2, a hollow vertical shaft 13 in the shape of an inverted funnel is provided on the table support portion 5a of a base platen and a tie bar 6 is secured within the shaft 13 in co-axial relationship to the shaft. The rotary table 14 is rotatably supported on the hollow shaft 13 by means of upper and lower ball bearings 15, 16. As more clearly shown in FIG. 3, the rotary table 14 has a center frame 17 in the shape of a regular triangle box and is provided with three mold opening and closing unit holding portions 18A, 18B and 18C each corresponding to each side of the triangle. The table 14 further has sector-shaped support boards 19A, 19B and 19C disposed between the adjacent mold opening and closing unit holding portions 18A, 18B and 18C, respectively. As more clearly shown in FIG. 4, a gear 20 is secured to the rotary table 14 and meshes a pinion 100 connected to the shaft of a motor 101 which is in turn secured to the table support portion 5a of the base platen 5. The motor 101 is driven by control means (not shown) to intermittently rotate the rotary table 14 by one third of its complete rotation at one time. When the rotary table 14 is to be stopped, a knock pin 102 having a tapered convex at the upper end is pushed up by a cylinder mechanism 103 provided on the base platen 5 so as to insert the knock pin 102 into a selected one of the tapered recesses 104a-104c of the same shape formed in the undersurface of the center frame 17 of the rotary table 14 whereby each mold opening and closing unit 29 can be stopped in proper alignment with the associated operation station.
The first station 2 comprises the base platen 5 integrally including the table support portion 5a of circular shape as seen in plane and a injection portion 5b of equilateral triangle shape as seen in plane. The base platen 5 is secured to a basement on the floor (see FIG. 2). And the tie bars 6, 7 are provided in upright disposition at the center of the table support portion 5a and at the opposite ends of the base of the equilateral triangle of the injection portion 5b, respectively. The upper ends of the tie bars 6 and 7 are inserted in tie bar holes (not shown) in a cylinder platen 8 of equilateral triangle and firmly held there by means of nuts 9. The first station 2 has the above-mentioned framework and is further provided with mold fastening means 10, injection means 11 and automatic molten metal supply means 12.
The second station 3 comprises a push frame 21 and a push cylinder frame 24. The push frame 21 has an equilateral triangle shape as seen in plane and is fixedly secured to the above-mentioned cylinder platen 8. The push cylinder frame 24 is fixedly secured to the table support portion 5a of the base platen 5 throuth a bracket 22. A tie bar 23 connects between the push cylinder frame 24 and push frame 21 (see FIG. 6). The second station 3 has the above-mentioned framework and is further provided with metal mold preparing means 25, product take-out means 26, a push cylinder 27 and a discharge cylinder 28 as more clearly shown in FIGS. 1 and 2. The metal mold preparing means 25 is adapted to present the mold opening and closing units 29 to mold opening and closing unit holding portions 18A, 18B at the time of start of the casting operation and metal mold replacement and take the unit out of the mold opening and closing unit holding portions 18A (18B, 18C). The metal mold preparing means 25 comprises a frame 30 secured to the floor and the frame 30 extends from below the mold opening and closing unit holding portion 18A (18B, 18C) which stops in the second station 3 towards the center line L2 of the second station 3. Further, a plurality of rollers 32 are disposed on the opposite sides of the upper surface of the above-mentioned frame 30 to be selectively rotated in forward and reverse directions from the motor 31 through a belt or chain (not shown).
Each mold opening and closing unit 29 holds a fixed metal mold 33 and a movable metal mold 34 and is adapted to move the movable metal mold to and away from the fixed metal mold.
Further, the third station 4 is not provided with the frame-work as provided in the first or second station 2 or 3, but comprises spray means 35 and insert means (not shown). The spray means 35 is adapted to clean the metal molds 33, 34 of the mold opening and closing unit 29 and spray release agent into the molds when the unit is newly installed on the rotary table 14 and after the product has been removed from such metal molds. The spray means 35 has an arm 38 and is supported by a frame 36. The arm 38 is advanced and reetracted by an oil pressure cylinder 37 and has a spray head 39 mounted at the leading end of the arm 38. In order to perform cleaning on the metal molds 33, 34, the arm 38 is advanced to position the spray head 39 between the metal mold 33, 34 whereupon air and release agent are spouted from the spray head 39 whereby the release agent is applied to the metal molds 33, 34. Reference numeral 40 denotes conventional core inserting means adapted to position a core (not shown) between the metal molds 33, 34. After the cleaning and other operations in the third operation station, the mold opening and closing unit 29 loosely closes the molds 33, 34 and is moved to the first operation station 2 as the rotary table 14 rotates by one third of its complete rotation and the above-mentioned mold closing and molten metal injection operation are performed in the first station 2.
The mold closing means 10 in the first station 2 comprises a cylinder 41 integral with the cylinder frame 8 and a main ram 43. The main ram 43 is received in the above-mentioned cylinder 41 and moves upward and downward under the pressure of oil introduced into the cylinder 41 throuth a port 42 formed in the cylinder 41. The main ram 43 has a moving platen 44 secured thereto. A pair of pull back cylinders 45 are secured to the upper surface of the cylinder platen 8 on the opposite sides of the above-mentioned cylinder 41 and the piston rod 48 of the pull back cylinder 45 extends through the cylinder platen 8 and is secured at the leading end thereof to the moving platen 44. With the above-mentioned arrangement of the components of the fastening means 10, when the main ram 43 is moved downward under the pressure of oil introduced into the cylinder 41, the metal molds 33, 34 loosely fastened by the mold opening and closing unit 29 are firmly fastened together under oil pressure. When oil is introduced into the pull back cylinder 43 after the removal of oil pressure, the moving platen 44 moves upward to thereby release the metal molds 33, 34 from the fastening force.
The injection means 11 comprises an injection cylinder 48 supported on tie bars (not shown) and a frame 47 depending from the base platen 5. The piston rod 49 of the injection cylinder 48 moves upward under the pressure of oil introduced in the cylinder and has a plunger 50 connected thereto by means of a coupling 51. The plunger 50 is received in an injection sleeve 54 which in turn moves upward and downward and is supported on a block 53 movable upward and downward by a ram 52. The injection sleeve 54 movable upwardly together with the block 53 by the ram 52 is received in a stationary sleeve (not shown) on the fixed metal mold 33 and the plunger 50 within the injection sleeve 54 moves upward by an injection cylinder 48 whereby molten metal within the injection sleeve 54 is injected into the cavity defined between the metal molds 33, 34.
The above-mentioned injection cylinder 48 can tilt to the position shown by the chain line L4 in FIG. 2 by means of tilting means (not shown). The automatic molten metal supply means 12 comprises a frame 55 provided on the base platen 5 extending uprightly therefrom and a main body 57 supported on the frame 55 through a four-joint link 56. Disposed below the main body 57 is a melting furnace 59 which rests on the floor. The above-mentioned main body 57 is provided at the leading end with a ladle 60 which is adapted to be inserted into the molten metal in the above-mentioned melting furnace 59 when a servo-motor 58 or the like drives to draw up the molten metal. The main body 57 moves to a position co-inciding with the chain line L4 by the 4-joint link 56 to supply the metal to the interior of the injection sleeve 54.
As the molten metal within the cavity is cooled to solidify, the pressurized oil is exhausted from the cylinder 41 through the port 42 and at the same time oil under pressure is introduced into the pull back cylinder 45 to raise the moving platen 44 whereupon the platen is released from the pressurizing action.
After the mold fastening under pressure, injection and pressure releasing operations in the first station have been completed, the mold opening and closing unit 29 holding the metal mold in its loose fastening condition is rotated to the second station 3 as the rotary table 14 rotates by one third of its complete rotation and stops in the second station where the metal molds are opened to take the product out of the molds.
The push cylinder 27 in the second station 3 comprises a piston rod (not shown) adapted to advance into the cavity defined between the metal molds 33, 34 under oil pressure. The product formed in the cavity is held on the movable metal mold 34 and the metal molds are opened. The discharge cylinder 28 in the second station 3 comprises a push pin (not shown) at the leading end of the piston rod which protrudes into the cavity in the movable metal molds 33, 34 and as the piston rod moves downwardly under the pressure of oil, the product is pushed out of the cavity.
The above-mentioned product removing means 26 receives the product pushed out of the cylinder and discharges the product onto the floor after cooling thereof. The product removing means 26 comprises a tray 62 and a puller 64 and is driven by an oil pressure cylinder 61. The tray 62 has a horseshoe shape. The tray 62 advances and retracts between the position shown and the central positions of the metal molds 33, 34. And the puller 64 advances and retracts in a direction at right angles to the tray 62. When the tray 62 which has received the product pushed out of the mold 34 in the advanced position retracts to the illustrated position, the puller 64 which is waiting in a position beyond the limit of advancement of the tray 62 retracts to pull the product from the tray 62 onto a cage 65. Although not shown, the cage 65 is provided with a link mechanism. When the link mechanism is moved by drive means (not shown), the cage 65 holding the product reciprocally moves between the position shown in FIG. 2 and a cooling tank (not shown) which cools the product in cold water contained therein. The cooled product slides down a chute (not shown) onto the floor. After the product has been discharged onto the floor, the mold opening and closing unit 29 moves to the third station 4 with the molds left open.
The above description is in connection with the step sequence when the single mold opening and closing unit 29 is provided in the rotary die casting machine. In the rotary die casting machine, each time the other mold opening and closing unit holding portions 18B, 18C stop in the second station 3, two additional mold opening and closing units 29 are attached to the mold opening and closing unit holding portions 18B, 18C whereby the three mold opening and closing units 29 are now mounted on the mold opening and closing unit holding portions 18A, 18B, 18C and the above-mentioned operations are then performed in the station 2, 3, 4 to perform the usual casting operation.
The operation for intermittently rotating and stopping the rotary table will be described hereinafter.
As shown in FIG. 3, the rotary table 14 rotates in the direction of the arrow and disposed below the rotary table 14 is a gear 20 having a cam or cams 120 integral therewith for driving the table as shown in FIGS. 4 and 5. The number of the cams 120 is equal to the number of the operation stations and accordingly, to the number of the stop positions. In the example illustrated, since the number of the stop positions is three, three cams 120a, 120b, 120c are disposed in a circumferentially equally spaced relationship. The front surface 131 of each cam 120 is formed with a plurality of recesses 133 as shown more clearly in FIG. 7. The recess 133 at the leading end of the cam 120 in the rotational direction of the same is wider than the other recesses.
Further, proximity switches 125, 126 are mounted on a base 123 in a vertically spaced relationship for detecting the associated cam 120 and the switch base is fixedly secured to a member such as the fixed base platen 5, for example (see FIG. 6). The upper proximity switch 125 is positioned in a level for detecting the front end face 131 of the cam 120 secured to the above-mentioned gear 20 by means of a bolt 121 and the lower proximity switch 126 is secured to a base 123 in a level for detecting the plurality of recesses 133 formed in the cam 120.
Thus, as the rotary table 14 rotates, when the cam 120 advances to approach the fixed upper and lower cam detection proximity switches 125, 126 in the direction shown by the arrow in FIG. 7 rightwards in the figure, the upper cam detection proximity switch 125 detects the edge 132 at the leading end face 131 of the cam 120. At this time, the fixed lower proximity switch 126 positioned below the upper proximity switch 125 is positioned on the first or leading recess 133 in the cam 120 and is still not detecting the cam edge 132. As the cam 120 continues to advance as shown by S1 in FIG. 8, since the leading end face 131 passes in a position very close to the cam detection proximity switch 125, the cam detection proximity switch 125 continues to detect the cam 120. On the other hand, as the lower detection proximity switch 126 is approaching the first edge 141 of the rearmost recess 133 in the cam 120, the switch 126 detects the cam 120 by means of the land 134 adjacent to the first edge 141 and then passes the next recess 133 without detecting the cam 120 and then again detects the cam 120 as the second edge 142 approaches the switch 126. In this way, the lower detection proximity switch 126 can repeatedly detect the cam 120 each time one land 134 of the cam 120 approaches the switch. That is, the upper cam detection proximity switch 125 produces a signal S1 confirming the presence of the cam 120 (120a-120c) and the lower recess detection proximity switch 126 produces a signal S2 by sensing the recesses 133 and convexes or lands 134 provided on each cam with equally spaced pitch P. By counting the number of pulse signals by a counter, the angular position of the rotary table 14 can be precisely known whereby the rotary table 14 can be stopped in any predetermined position at a predetermined rate of deceleration.
That is, each cam 120 and the recess detection proximity switch 126 form means for detecting the angular position of the rotary table 14 and the cam is unevend to form a plurality of recesses 133 and the switch 126 produces a signal having a plurality of pulses by detecting the recesses and lands 133, 134 in succession (FIG. 8). As more clearly shown in FIG. 10, the pulse signal S2 is fed to a counter 135 which counts the pulse signals S2 to operate a controller 136 which in turn controls and operates a flow rate control valve 140 to thereby decelerate the rotational speed of the rotary table 140. For example, the pulse signals S2 produced from the position detector for decelerating the rotary table 14 per pulse decelerates the rotary table 14 from the high speed V1 per pulse and the rotary table 14 is stopped when the recess detection proximity switch 126 detects a predetermined recess 133 out of all the recesses 133 formed in the cam 120 (see FIG. 9).
Thus, the rotary table 14 can be precisely stopped in a predetermined position referring to the recesses 133 formed in the cam 120.
FIG. 8 respectively shows the output signal S1 from the cam detection proximity switch 125 and the output signal S2 from the recess detection proximity switch 126 when the cam 120 is rotated at a constant rotational speed.
The cam detection proximity switch 125 outputs a signal sooner than the recess detection proximity switch 126 by a time t1 during which time the rotary table 14 moves by the distance covering the length L1 of the first recess 123 at the leading end portion of the cam 120 and terminates the production of signals later than the recess detection proximity switch 126 by a time t2 during which the rotary table 14 moves by the distance covering the length L2 of the portion of the cam following the last recess 133.
Thus, by the utilization of the rise of detection signals from the cam detection proximity switch 125, the counter 135 counting pulse signals of the above-mentioned recess detection proximity switch 126 can be easily reset. The position detector can be easily designed so that only during the time period the cam detection proximity switch 125 is detecting the cam 120, does the recess detection proximity switch 126 count the recesses and/or lands 134. If the counter 135 is always reset before the recesses 133 are counted by the recess detecting proximity switch 126, even if the counter 135 counts erroneously due to noise produced during the time period the counter 135 is not counting, it is made possible that the counter 135 is not subjected to adverse effects when the counter 135 in fact counts whereby deceleration and stopping of the rotary table 14 can be more positively controlled.
Further, the hydraulic pressure circuit shown in FIG. 10 is divided into a direction switching valve 139 and a flow rate control valve 40 which controls displacement flow rate from the hydraulic motor 101. The flow rate control valve 140 is the subject of the co-pending Laid-Open Japanese Patent application Publication No. 57-6863 in the name of the present application. The flow rate control valve 40 rotates a ball screw 142 by means of a pulse motor 141 as shown in FIG. 11 and the ball screw 142 moves a nut shaft 143 back and forth so that the nut shaft 143 directly drives a valve spool 144. As described hereinabove, output signals in pulse form to be detected by the recess detection proximity switch 126 are input to the counter 135 and the count value of the counter 135 directly controls the opening and closing speed of the valve spool 144 of the flow rate control valve 140 so that the operation of the flow rate control valve 140 decreases the opening of the flow rate control valve 140 in succession each time the recess detection proximity switch 126 detects the recesses 133 formed in the cam 120 fixedly secured to the rotary table 14.
A brake circuit 114 is constituted by a check valve 115 and a relief valve 118 and the brake circuit 114 is a conventional pressure adjusting circuit adapted to prevent occurrence of abnormal pressure in the hydraulic circuit.
In controlling the deceleration and stopping of the rotary table 14 by controlling the rotational speed of the rotary table 14 while detecting the recesses in the cam 120 by the recess detection proximity switch 126, in order to precisely stop the rotary table 14 in a predetermined stop position, it is necessary to reduce the pitch P of the recesses and lands. In order to precisely detect the recesses and lands of a cam having a small pitch P of the recesses and land by the recess detection proximity switch 126 it is necessary that the recess detection proximity switch 126 is provided as near as possible to the surface of the cam 120.
However, in a large size apparatus such as the rotary die casting machine of the instant invention in which the rotary table 14 has an outer diameter of about 6 m and in which a plurality of mold opening and closing units 29 of several tons are employed, as shown in FIG. 6, the allowable minimum clearance l between the cam 120 and proximity switch 126 is 1 mm. Further, the allowable minimum P of the recesses and lands is about 10 mm (the width of the lands 134 and recesses 133 is about 5 mm).
The reason why the allowable minimum clearance l between the cam 120 and recess detection proximity switch 128 is defined as being 1 mm is that the diameter of the bearings supporting the rotary table 14 is 1 m and the size tolerance of the bearings supporting the table is about 0.1 mm to 0.3 mm. Furthermore, when the mold opening and closing units 29 each having a weight of about 30 to 50 tons are mounted onto and demounted from the rotary table 14, distortion of the order of about 0.1 to 0.2 mm occurs on the rotary table 14. The minimum limit of the pitch P is because the easily available recess determination proximity switch having a limited discrimination capacity can not discriminate between the recess 133 and lands 134 when the clearance between the recesses and lands is below about 10 mm.
Taking errors in mounting, adjustment and maintenance of the position detector into consideration, the practical limit of the pitch P is about 15 mm at which limit fine detection of the rotary table becomes difficult and enhancement of precision in table position detecting cannot be attained.
In addition, there is the drawback that when the distance between the cam 120 and proximity switch 126 increases due to occurence of distortion of the rotary table 14, the timing for detecting a selected recess 134 and producing a signal by the recess detection proximity switch 126 delays to thereby make it difficult to precisely detect the angular position of the rotary table 14.
Further, the final positioning of the rotary table 14 is performed by inserting the knock pin 102 into a selected one of the tapered recesses 104a-104c formed in the undersurface of the table 14 if the rotary table 14 has a diameter of several m, because of error in forming the tapered recesses 104a-104c, even when the operation stations are disposed in an equally spaced relationship to thereby control the braking and stopping of the rotary table 14, when the knock pin is inserted into any one of the tapered recesses 104a-104c, there is the drawback that tremor occurs in the rotary table 14 due to a deviation in position of the tapered recesses 104a-104c resulting in the occurrence of impact.